This invention relates to a badminton racket.
Badminton players generally are required to carry-out more nimble, high-speed swing actions to bat a shuttle cock at short intervals in a relatively small court space compared with, for example, the game of tennis. This nimbleness and speediness is the very characteristic of the badminton game. Therefore, it becomes necessary for the badminton racket to be so constructed as to satisfy the players' nimble and high-speed actions. To this end, the badminton racket is required to be light in weight and have satisfactory resilience for easy handling. Furthermore, in order to satisfy the need for a high-speed swing action which is the most important feature of the badminton game, the dimensions of the badminton racket in the swing direction must be minimized. In other words, air resistance must be minimized as much as possible. At the same time, it is necessary to provide the racket with a high mechanical strength in order withstand the stress of a high-speed swing as well as various impact loads arising from the use of the racket. Although these are all indispensable factors for a good badminton racket to possess, it is very difficult to fulfil all of them simultaneously, since some of them are incompatible with others. For example, light weight, desirable resilience and minimum air resistance may all be provided together in the badminton racket, but all these factors result in the reduction of the mechanical strength thereof. Unless a good balancing of the incompatible factors can be provided, any other improvement in the structure of the badminton racket would be meaningless.
In order to satisfy the foregoing requisites as much as possible, the badminton racket has been carefully designed to take its present style and structure. That is, the badminton racket has taken completely different historical steps of development from other similar rackets, such as a tennis racket, designed to hit a heavier ball. At present, as shown in FIGS. 1 (a), 1 (b) and 1 (c), a badminton racket formed of a rigid tubular shaft 1 and a tubular frame 2 connected with each other by a tubular joint 3 of substantially T-shaped configuration represents the main stream of badminton racket design. The badminton racket of this type has the frame 2 made of a tubular material having light and resilient properties such as, for example, fiber reinforced plastic (hereinafter referred to as "FRP"), stainless steel or aluminum, and connected to the shaft 1 by means of the T-shaped tubular joint 3 as shown in FIG. 1 (a). The shaft 1 is constructed of tubing of circular cross section as shown in FIG. 1 (b), while the frame 2 is of tubing of irregularly rounded cross section, as shown in FIG. 1 (c), having a major axis thereof disposed in the swing direction which is perdendicular to the racket face. This conventional badminton racket is thus constructed with a view to achieving high mechanical strength to meet the requirements of a high-speed swing, in addition to light weight, reduced air resistance and satisfactory resilience.
A badminton racket with the above structure has been considered to be very close to an ideal style until recently. However, actually, there remained a number of problems yet to be solved. Firstly, with such badminton racket, the above mentioned T-shaped joint portion is inherently required to be constructed with larger dimensions than the other racket portions. Specifically, with such conventional badminton racket, the tubular joint 3 is adapted to connect frame 2 and shaft 1 and is formed substantially in a T-shaped configuration having portions 3a--3a and 3b in which terminal ends 2a--2a of the frame 2 and the upper end 1a of the shaft 1 are fixedly inserted, respectively, as shown in FIGS. 2 (a) to 2 (c). However, since the outer diameter of this joint portion 3 is much larger than those of the shaft 1 and the frame 2, air resistance becomes much larger. The air resistance applied to the joint portion 3 has been a large obstacle for reducing the air resistance of the racket as a whole. To be worse, the present inventor learned that, since the joint 3 forms a pivotal portion at which various loads arising from the swing of the badminton racket are structurely concentrated, any effort to minimize air resistance by decreasing the size and thickness of portions 3a, 3b, will lead to a decrease of the mechanical strength of such pivotal portion. Because of the reasons set forth above, a sufficiently large size and thickness of the joint portion 3 had to be maintained, even at the sacrifice of the requirement to decrease the air resistance.
Furthermore, the tubular T-shaped joint 3 is found to be a large obstacle to achieving desired resilience of the badminton racket. In other words, since the joint 3 is a pivotal portion for joining the frame 2 and the shaft 1, it is required to be of sufficient mechanical strength, while the provision of such mechanical strength of tubular joint 3 may prevent the badminton racket from having satisfactory resilience. When the mechanical strength of the joint 3 is increased while maintaining satisfactory resilience of the racket, the shaft 1 and the frame 2 will be subject to material fatigue, primarily at portions thereof adjacent the end portions 3a, 3b of the T-shaped tubular joint 3, due to the concentration of various impact loads resulted from the difference in rigidity and resilience therebetween. This will result in easy breakage of the shaft and the frame at such portions.
As mentioned in the foregoing, in the conventional badminton racket, there are too many factors which are incompatible with each other, although they are very important for a desirable function of the badminton racket shown. The conventional badminton racket in FIGS. 1 (a) through 2 (c) cannot satisfy all these factors, i.e., high mechanical strength, minimum air resistance and desirable resilience, simultaneously.